The inefficiency of fossil-fuel prime movers currently being used in propulsion systems for automotive vehicles is well known. For example, the gasoline internal combustion engine has an efficiency of approximately 22%, whereas the diesel internal combustion engine has an efficiency of approximately 35%. When one also considers the mechanical losses that result from the use of a variable-ratio, mechanical transmission and other elements for coupling the fossil-fuel prime mover to the driving wheels of the automotive vehicle, it can be seen that the overall efficiency of the vehicle, in extracting energy from fossil fuels and delivering the extracted energy in the form of rotational motion of the driving wheels, is quite low.
It has been known for many years that electric motors are capable of very high efficiencies in converting electrical energy into mechanical energy. Accordingly, many types of electric propulsion systems for automotive vehicles have been proposed. In such systems, electrical energy is obtained from an electrical energy source, typically a bank of rechargeable batteries, and is converted by an electrical motor into rotational motion of an output shaft of the motor. The output shaft is coupled to the driving wheels through a variable-ratio mechanical transmission, universal joints, and the like, in order to permit efficient energy conversion over a plurality of predetermined speed ranges. Such electric propulsion systems are additionally advantageous over propulsion systems using a fossil-fuel prime mover in that regenerative braking can be accomplished by causing the electrical motor to act as a generator, whereby a portion of the energy developed during braking, normally lost as heat by the mechanical brakes of the vehicle, is fed back to the electrical energy source.
For a number of reasons, electric propulsion and braking systems for automotive vehicles have found only limited acceptance. One of these reasons is the lack of significant energy storage capacity of currently-available rechargeable batteries. As a result, a large bank of such rechargeable batteries must be used in order to achieve an acceptable operation range for the vehicle. Although other electrical energy sources, such as the hydrogen fuel cell, have been proposed which are capable of providing more electrical energy per unit of size and of weight, such other electrical energy sources have not been heretofore available in inexpensive, production quantities.
Because of the large number and weight of rechargeable batteries that are required, the electric propulsion and braking system must be compact in size and low in weight in order to develop an overall efficiency of energy conversion for the vehicle which is significantly superior to that currently available from propulsion systems using fossil-fuel prime movers.
In order to propel an automotive vehicle of average size at freeway speeds, and to provide adequate reserve power for maintaining freeway speeds under varying grade conditions and for passing, the electrical motor should have a horsepowr capacity in the range of 40-60 horsepower. Unfortunately, currently available electric motors of this horsepower capacity are too large and bulky for use in an automotive vehicle, particularly when the size and bulk of the rechargeable batteries and of the variable-ratio mechanical transmission are also considered. Therefore, electric propulsion and braking systems typically use a smaller electrical motor and have been incorporated only in automotive vehicles which are capable of maintaining fairly low speeds over a limited range of operation.
It is therefore an object of this invention to provide an improved electric propulsion and braking system for automotive vehicles.
It is another object of this invention to provide a system which has an efficiency of electrical-mechanical energy conversion significantly greater than that accorded by previous electrical propulsion and braking systems.
It is yet another object of this invention to provide such a system which permits an automotive vehicle in which the system is installed to be capable of running at freeway speeds over an extended operating range, with adequate reserve power for maintaining freeway speeds and for passing.
It is a further object of this invention to provide such a system which affords gross speed and power range control for rotating and braking the wheels of an automotive vehicle through control of electrical energy transferred between a plurality of electrical motors each directly coupled to a wheel of the vehicle and a plurality of electrical energy sources.
It is yet a further object of this invention to provide such a system in which electrical-mechanical energy conversion is accomplished by controlling energy flow between the electrical energy sources and the electrical motors through the use of a programmed microprocessor.
It is still a further object of this invention to provide an electric propulsion and braking system which is smaller and lighter than the electric propulsion and braking systems of the prior art.